Methods for establishing and maintaining communications within wireless communication systems are well known in the art. In U.S. patent application Ser. No. 08/640,291 entitled "Method For Providing Communications To A Communication Device In A Radio Communication System" by Capurka, filed Apr. 30, 1996 and assigned to the same assignee as the present invention, a technique is described wherein a communication device (e.g., a portable or mobile radio), while roaming within a wireless communication system, registers with individual base sites and location areas (each location area encompassing the coverage areas of one or more base sites).
When a communication (e.g., a packet data communication) destined for the communication device is received by a system controller, the system controller determines whether the communication was received within a predetermined period of time after a previous communication involving the communication device. When the communication is received within this predetermined period of time, the system controller transmits at least a portion of the communication to the communication device via the base site.
However, when the communication is received subsequent to the predetermined period of time, the system controller transmits a page to the communication device via the base sites serving the location area to inform the communication device of the awaiting communication. Upon receiving an acknowledgment of the page, the system controller transmits the communication, or a portion thereof, to the communication device via the base site that received the acknowledgment. In this manner, Capurka substantially reduces the amount of control channel activity (i.e., paging) normally associated with delivering a communication by presuming that the communication device has not moved out of the coverage area of the base site for a predetermined amount of time after the communication device's involvement in a previous communication.
In effect, Capurka describes the concept of a session wherein communications with a given communication device are carried out in one manner while a session is in progress, and are carried out in another manner when a session is not in progress. The maintenance of each session is predicated on the occurrence of events within the predetermined period of time. Both the system controller and the communication device keep track of the predetermined period of time, thereby independently determining whether a session is still in progress. However, due to variable delays within the infrastructure of the communication system, it is possible that the system controller and communication device may lose synchronization in measuring the predetermined period of time. As a result of this, communications with the communication device may be delayed or even lost. For example, if the controller times out of a session prematurely and receives an outbound communication destined for a communication device, the outbound communication will not be sent to the mobile directly. Because the controller believes that the communication device is not in session, the device will be paged to announce the pending communication, leading to inefficient use of communication resources. Also, because the communication device is still within a session, it will be monitoring a traffic channel, rather than a control channel, and will quite likely miss the page and the subsequent outbound communication altogether.
Therefore, a need exists for a method of maintaining session synchronization between a communication device and a system controller.